1. Field of the Invention
The present invention relates to a process for producing aromatic isomers by adsorption separation and to an adsorbent used therefor.
2. Description of the Related Arts
As processes for separation of aromatic isomers, particularly halogenated aromatic isomers, rectification, cryogenic separation, and adsorption separation are known so far. The present invention relates to a process for adsorption separation.
Separation by rectification suffers the disadvantage of requiring a rectifying column with a large number of plates because halogenated aromatic isomers differ from one another only slightly in boiling point. Cryogenic separation suffers the disadvantage of requiring valuable equipment and high energy costs for cooling. In order to eliminate these disadvantages, processes for adsorption separation have been studied and developed. Japanese Patent Publication No. 5155/1962 discloses that an adsorbent prepared by introduction of alkali metal ions or alkaline earth metal ions into zeolite X can be used for separation of halogenated aromatic isomers. Japanese Patent Laid-Open No. 105434/1978 discloses a process for separation of specific isomers from a mixture of dichlorobenzene isomers by means of an adsorbent prepared by introduction of Cs or Rb ions into zeolite Y. Japanese Patent Laid-Open Nos. 31627/1982, 35528/1982, and 191933/1982 disclose a process for adsorption separation of chlorotoluene isomers by means of K ion-exchanged zeolite Y as an adsorbent. Japanese Patent Laid-Open Nos. 131923/1983 and 176223/1984 respectively disclose Ag ion- and K ion-exchanged zeolite Y and Na ion- and Cu ion-exchanged zeolite Y to be used as an adsorbent for separation of m-chlorotoluene.
These adsorbents permit separation of aromatic isomers but their performance is not satisfactory.